1. Field of the Invention
The invention pertains to air quenching systems for heated parts characterized by its ability to uniformly cool the heated part throughout its configuration and regulate the rate of cooling during air quenching.
2. Description of the Related Art
Metal parts, usually formed of steel alloys, are commonly heat treated to improve the wear and strength characteristics of the part. The heat treating of metals is highly complex with the resultant wear and strength characteristics being determined by the percentages of carbon and other materials within the steel, or other metal, the rate of cooling, and the composition of the cooling medium. It is common to cool heated parts by the use of an oil bath quench wherein the part is rapidly cooled and the heat treatment characteristics are determined by the variables mentioned above.
While oil bath quenching is commonly used for heat treatment purposes, it is also common to use an air quench or cooling chamber utilizing moving air, to cool the heated part. Air quenching has the advantage of producing a slower cooling of the part than achieved with an oil bath quench, or the like, but, henceforth, it has been difficult to control air quenching procedures other than varying the length of time that the heated part remains in the cooling air stream.
When heat treating certain steels, particularly forgings, to produce critical parts, such as the connecting rods of internal combustion engines, in order to achieve the desired strength and wear characteristics, the selection of the steel composition is important, as is the heat treatment. The durability and strength of a part such as an engine connecting rod depends on the formation of carbon or carbide into a fine grain whose particles are rounded. Grain formation is achieved by elevating the steel temperature above 2200.degree. F. wherein the carbide readily disburses throughout the steel, followed by slow cooling to atmospheric temperature. Slow cooling such as produced in air quenching systems produces the required pearlite grain structure necessary to achieve the desired connecting rod characteristics. To rapidly quench engine connecting rods in an oil bath produces a martensite grain which is significantly harder and more brittle than the pearlite grain structure desired.
Previously, air quenching systems have not been available wherein the heated part can be uniformly cooled by air, and wherein the rate of cooling during the cooling process could be closely controlled to consistently achieve the desired metal grain structure.